TIM FURNISS / LONDON
Meanwhile, a Boeing Delta II adds in-orbit spares to Iridium mobile communications satellite constellation
Boeing's Delta II and Orbital Sciences' (OSC) Pegasus XL launch vehicles successfully made their first 2002 launches earlier this month. The Pegasus carried NASA's delayed High Energy Solar Spectroscopic Imager satellite (HESSI) and the Delta II boosted the Iridium satellite constellation.
A Pegasus XL booster, deployed from OSC's Lockheed L1011 TriStar operated from Cape Canaveral, air-launched HESSI on 5 February, marking the start of NASA's Small Explorer spacecraft programme. The 295kg (650lb) spacecraft was placed into a 600km (370 mile) circular orbit, inclined at 38° to the equator. HESSI will study high energy X-ray and gamma-ray solar flares, and return high-fidelity images over a two-year, $85 million mission.
HESSI was scheduled for a launch in July 2000, but this was postponed after the satellite was damaged during vibration testing. It encountered a further delay after a Pegasus launch failure last year.
Less than a week after the Pegasus launch, a Boeing Delta II booster carried five Iridium mobile communication satellites from Vandenberg AFB, California. These craft will serve as in-orbit spares for the new Iridium Satellite company, which took over the former Motorola-led bankrupt project in December 2000. Iridium Satellite provides services to the US Department of Defense under a multi-year contract and is working with20 service partners to sell and support services globally. Delta IIs launched 55 of the original Iridium satellites between May 1997 and November 1998.
NASA plans to use a Delta II to demonstrate a tether-based propulsion system that could be used to de-orbit spent rocket stages or to transfer orbits. A Delta II launch this summer will deploy the second stage fitted with a Propulsive Small Expendable Deployer System (ProSEDS) to demonstrate an electrodynamic tether's ability to generate significant thrust to replace the use of chemical propulsion systems to raise or lower orbits. The 5km-long ultra-thin bare-wire ProSEDS conducting tether will be connected to a 10km non-conducting tether. The movement of the conductor through the Earth's magnetic field will generate an electrical current (the same principle as an electric dynamo) which will then be emitted into space through a plasma contactor, completing the electrical circuit and generating thrust.Source: Flight International
